The present invention relates to an improvement in a vane pump.
A vane pump is of a type such that suction and discharge of a fluid are performed by revolution of vanes in slide-contact with the inner circumferential surface of a housing, the vanes being projected from a rotor due to centrifugal force resulted when the rotor is rotated.
FIG. 1 is a sectional view of a conventional vane pump and FIG. 2 is a sectional view taken along the line II--II' in FIG. 1. A reference numeral 1 designates a motor for driving the vane pump, which comprises a frame 1a and a rotary shaft 2 pivotally supported by the frame 1a. A rotor 3 is fixed to the rotary shaft 2. A plurality of vanes 4 are respectively held in grooves formed in the rotor 3 in the radial direction so as to be slidable along the grooves. The rotor 3 with the vanes 4 is received in the inner space of a housing 5, the inner space of the housing having a cylindrical inner circumferential surface the center of which is deflected from the center of the rotary shaft 2, i.e. the rotor 3. At both sides of the housing 5, arranged are a side plate 6 and a cover plate 7 which form an operating chamber 8 in association with the rotor 3. An intake port 9 and a discharge port 10 are respectively provided at different positions in the outer circumferential part of the housing 5 to be communicated with the operating chamber 8 formed in the housing 5. The housing 5, the side plate 6 and the cover plate 7 are secured to the frame 1a of the motor 1 by means of a fitting bolt 11. A sealing member 12 is fitted to the frame 1a to be in relative slide-contact with the rotary shaft 2.
In the vane pump having the construction as above-mentioned, upon actuating the motor 1, the rotary shaft 2 is rotated in the direction of the arrow mark along with the rotor 3 mounted on the rotary shaft 2. The rotation of the rotor 3 causes the vanes 4 which are slidably held in the grooves formed in the radial direction of the rotor 3 to project outward due to centrifugal force and to move in slide-contact with the inner circumferential surface of the housing 5. In this case, the inner space of the housing 5 is in an eccentrical relation to the rotor 3 whereby as the rotor 3 rotates, the capacity of the operating chamber 8 defined by the vanes 4 is changed. Namely, there is a boundary in the inner circumferential surface portion of the housing 5, the boundary being at the closest position to the axial center of the rotary shaft 2. The capacity of the operating chamber 8 increases for 180.degree. revolution of the rotor 3 and the capacity decreases for the subsequent 180.degree. revolution of the rotor. Accordingly, a fluid is sucked from the intake port formed at one side with respect to the boundary at the inner circumferential surface portion of the housing 5 which is the nearest to the axial center of the rotary shaft 2 and the fluid thus sucked is discharged through the discharge port 10; thus, pumping operations is obtainable.
When the vane pump as above-mentioned is used for an air source for a burner, it is necessary to produce a primary air of a high pressure and a small flow rate to atomize fuel and a secondary air of a low pressure and a large flow rate to perform combustion of fuel. However, in the construction of the conventional vane pump, when the primary and secondary air are to be supplied with a single pump, air having a high pressure and a large flow rate are needed to result in increase in the capacity of the pump. And also, a controlling mechanism for supplying the primary and secondary air becomes very complicated. Accordingly, when the vane pump is used for an air source for a burner, two separate vane pumps for the primary air supply and the secondary air supply are needed with the result of increase in manufacturing cost.
The vane pump is used as a vacuum pump to impart vacuum condition to a vacuum servo brake of cars. Also, it is used as an air pump for recombustion of an exhaust gas of cars or for supercharging a thin air to the engine. The principle of operations of both the pumps is identical. However, a vacuum pump sucks fluid from a load side unless a brake is operated. On the other hand, the air pump always supercharges air to the engine. Accordingly, condition of fluid in the vacuum pump and the air pump is opposite each other. It is therefore necessary to use two pump devices independently when vacuum condition and supercharging condition are simultaneously needed.
In a car, there are two types of load sources for the vacuum pump, namely the vacuum servo brake consuming a great quantity of vacuum at the time of operating the brake and a chamber of a constant speed driving device which always requires a small quantity of vacuum in its operation. Accordingly, if a single vacuum pump is used, the vacuum condition is always needed by the constant speed driving device and occasionally, a great quantity of vacuum is consumed by braking operation. In latter case, charging of vacuum becomes short to thereby cause adverse effect to braking performance. To avoid of such problem, a large capacity vacuum pump with a vacuum tank for storage of the vacuum condition is needed.
A car should be provided with a vacuum pump used to supply a vacuum to a vacuum servo brake and an oil pump used for a hydraulic system for power stirring of cars and adjustment of the height of cars. Therefore, two kinds of fluid i.e. air and oil have to be controlled. A vacuum pump and an oil pump are respectively required for these purposes. Although the structure and principle of the operations of the pumps are identical.